A persistent belief emerged concerning certain dinosaurs and their neurological makeup: that some colossal animals might have housed more than one brain. This concept fueled widespread curiosity and became a notable piece of dinosaur lore. This article explores the origins of this popular idea, examining the scientific observations that initially gave rise to it and clarifying what modern research reveals about the true anatomy of these magnificent beings.
The Dinosaur at the Center of the “Two Brains” Idea
The Stegosaurus, a large, armored herbivore from the Late Jurassic period, is most famously associated with the “two brains” theory. Early paleontological studies by Othniel Charles Marsh revealed an unusual anatomical feature: an enlarged cavity within the spinal column in its pelvic region. This cavity was notably larger than the animal’s brain in its skull.
Given the immense size of Stegosaurus—up to 30 feet long and weighing 5 to 10 tons—and its comparatively small head-brain, this large sacral cavity led to speculation. It was theorized that this expanded area functioned as a “second brain,” perhaps to assist in controlling the massive hindquarters and tail. This hypothetical posterior brain was believed to coordinate movements or process sensory information more efficiently for the animal’s large rear section.
What the “Second Brain” Really Was
Despite early theories, the enlarged cavity in the pelvic region of Stegosaurus was not a second brain. Modern scientific understanding indicates this space was an expanded part of the spinal canal, often referred to as a sacral enlargement. This area likely contained a large neural ganglion, a cluster of nerve cells, and potentially a glycogen body. The glycogen body, also found in modern birds, serves as a reservoir for energy-rich glycogen, providing metabolic support for the nerve network and powerful muscles of the hind limbs and tail.
This complex neural network facilitated reflexes, coordinated movements, and processed sensory input for the dinosaur’s large posterior. It was a specialized adaptation for managing the physical requirements of such a large body, particularly in controlling the tail, which in Stegosaurus was equipped with formidable spikes known as thagomizers. This enlargement did not possess the cognitive capabilities of a true brain, distinguishing it as a functional neural hub rather than a center for thought or decision-making.
Why the Myth Persisted
The notion of a dinosaur with two brains gained traction and endured in popular culture for several reasons. In early paleontology, understanding of dinosaur neuroanatomy was limited, leading scientists like Othniel Charles Marsh to offer speculative interpretations for unusual anatomical findings. The intriguing nature of a creature possessing two brains made it a memorable and appealing concept to the public, easily disseminated through popular articles and books.
Even after scientists, including Marsh, began to question and abandon the “second brain” hypothesis due to a lack of confirming evidence, the narrative had already taken root. Scientific findings often take time to filter into widespread public understanding, allowing incorrect ideas to persist. Modern imaging techniques and comparative anatomical studies have definitively disproven the two-brain theory, yet its enduring presence highlights the influence of stories in shaping popular perceptions of prehistoric life.